1. Field of the Invention
The present invention relates to an information storage medium and a method of recording and erasing information in and from the information storage medium, wherein information is recorded/erased by inducing a phase change in a portion irradiated with a light beam such as a laser beam, and the information is reproduced by detecting a change in optical characteristic such as reflectivity or transmittance upon this phase change. Information storage media used in such a method are, e.g., an optical disk, an optical card, an optical tape, and optical drum.
2. Description of the Related Art
A phase-transformation type information storage medium is well known as an information storage medium capable of erasing information such as a so-called erasable optical disk. This phase-transformation type information storage medium includes a substrate made of, e.g., glass or a plastic material (a polycarbonate resin, a polymethylmethacrylate resin, or the like), and a recording layer formed on the substrate. As materials for this recording layer, chalcogenide alloys such as GeTe are known. When light beams having different conditions (e.g., a laser beam) are radiated on these materials, these materials are reversibly transformed between two phases, e.g., crystalline and amorphous phases. Information can be recorded and erased by using these phase transformations, and can be read by using changes in optical characteristics such as reflectivity and transmittance upon these phase transformation.
Materials which are suitable for such a recording layer are materials having eutectic compositions in which phase transformations are easily caused by radiating light beams, or materials for intermetallic compounds.
A conventional method of recording and erasing information by using a phase transformation between crystalline and amorphous phases, which method has been applied to phase-transformation type information storage media, cannot satisfactorily ensure the characteristics of an information storage medium. Especially, a strong demand has arisen for a method of recording and erasing information at a higher speed and allowing a single-beam overwrite operation.